Livestock Research for Rural Development 15 (9) 2003

Citation of this paper

Incidence and modulating effects of environmental factors on trypanosomosis, peste des petit ruminants (PPR) and bronchopneumonia of West African dwarf goats in Imo state, Nigeria

I C Okoli

Tropical Animal Health and Production Research Laboratory
Department of Animal Science and Technology, Federal University of Technology
PMB 1526, Owerri, Imo state, Nigeria.
dr_charleso@yahoo.com


Abstract

Clinical records of natural infections of trypanosomosis, peste des petit ruminants (PPR) and bronchopneumonia among West African Dwarf (WAD) goats brought for treatment at government veterinary clinics in Imo state, Nigeria were scrutinized for three years (1999-2001) in order to determine disease trends and modulating effects of rainfall, relative humidity and mean daily air temperature on disease occurrence.

Of the 26763 such cases, 14824 (55.4%) were due to trypanosomosis, while 25.09% (6714) and 19.5% (5225) were accounted for by bronchopneumonia and PPR respectively, indicating a significantly lower treatment figure for PPR (p<0.05). Overall, treatment figures across four seasons stayed above 6000 cases per season. However, the 4375(29.5%) cases of trypanosomosis recorded during early dry season were significantly (p<0.05) higher than those of other seasons. Treatment means for PPR (22.8%) during late wet season and late dry season figures for bronchopneumonia (33.5%) were significantly (p<0.05) higher than those of other seasons. Simple correlation matrix of mean monthly disease occurrence showed that trypanosomosis and bronchopneumonia tended to vary together 41.0% of the times while for PPR and bronchopneumonia it was 44.0% indicating a moderate association between these diseases. Occurrence of trypanosomosis became lower during the heavy rainfall, high humidity and lower daily air temperature months (July to September) while more cases of PPR and bronchopneumonia were recorded during the dry months of December to January.

Contrary to published reports; trypanosomosis remained the most common of the diseases encountered in WAD goats treated at Imo state veterinary clinics.

Keywords: bronchopneumonia, clinical records, Nigeria, PPR, trypanosomosis


Introduction

High incidence of infectious diseases constitutes a major impediment to livestock production in most developing countries. However, technological difficulties in these countries hinder extensive use of modern diagnostic techniques in disease surveillance. Clinical records and abattoir slaughter figures are therefore greatly relied upon as sources of information for disease prevalence studies. For example, clinical records have been used in monitoring trends in diseases of economic and public health importance in Africa and different agro-climatic zones of Nigeria (Abdu et al 1985; Mboera and Kitalyi 1994; Halle et al 1998; Nwanta et al 2000).

These studies are usually restricted to the analysis of prevalence rate and evaluation of seasonal influence on disease trends. Limited attention is paid to possible interaction between the different disease agents or their symptoms. For example, a recent analysis of abattoir data by Okoli et al (2002) showed that linear response of emaciation to fascioliasis in sheep was significant at 5% level giving the impression that 70% of the variations because of emaciation could be accounted for by a linear function involving influence of fascioliasis. Furthermore, many animal disease agents require certain optimal ecological factors such as rainfall, relative humidity and temperature for survival in their environment and for the production of disease symptoms in the host. It is therefore important to understand not only the interactions between different diseases occurring in the same environment, but also the modulating influence of the climatic factors driving the seasonal variations usually observed (Onwuliri et al 1993). Such knowledge is essential in planning control strategies against infectious diseases.

PPR, pneumonia and parasitic gastro-enteritis are mentioned as the three most important causes of mortality in small ruminants in humid tropical West Africa (Akerejola et al 1979; Sumberg and Cassaday 1985). Trypanosomosis on the other hand, is reported to produce a mild disease of limited importance in small ruminants under natural conditions (Spephen 1970). Recent epidemiological studies are however revealing new trends of this infection among this class of food animals in Nigeria (Kalu et al 1991;Osho et al 2002). This paper reports on the incidence and modulating effects of environmental factors on clinical cases of trypanosomosis, PPR and bronchopneumonia among WAD goats brought for treatment at veterinary clinics in Imo state, Nigeria from 1999 to 2001.


Materials and methods

Study area

Imo state is situated in the south-eastern rain-forest vegetational belt of Nigeria. It lies between latitude 5 4' and 6 3' N and longitude 6 15'and 7 34' E. The area is dominated by plains 200m above sea level except for elevations associated with the Okigwe uplands (Ofomata 1975). It has an annual rainfall of about 1700mm to 2500mm, which is concentrated almost entirely between March and October. Average humidity is about 80%, with up to 85% occurring during the rainy season. The mean daily maximum air temperatures range from 28C to 35C, while the mean daily minimum ranges from 19C to 24C.

In this rain-forest zone, smallholder livestock production predominates, with over 80% of rural families keeping West African Dwarf (WAD) ruminants and mixed breeds of local and exotic chicken (Molokwu 1982; Ejiogu 1990) primarily as sources of investment, manure and meat at home or during festivals. In most parts of the state, WAD goats are allowed to roam throughout the seasons, thriving on indigenous browses growing in compound bushes and farm fallows with additional supplementation from kitchen wastes (Okoli et al 2003). Prophylactic management of common infectious diseases is rarely practiced.

Data collection

Data on clinical cases of trypanosomosis, PPR and bronchopneumonia among WAD goats brought for treatment at government veterinary clinics at Imo state, Nigeria were scrutinized for three years (1999-2001). The treatment records were collected from the public health unit of the federal livestock department (FLD) Imo state zonal office. Diagnoses at the veterinary clinics are usually based on flock history, clinical signs, necropsy findings and laboratory results. The confirmatory tests for trypanosomosis involve buffy coat and thick blood smear demonstration of the parasites, while for PPR, a simple agar gel diffusion test usually suffices.

Clinical records for the state are usually generated through routine clinical activities of state veterinary personnel who cover all the official clinics in the different local government areas. Data from the local government areas are pooled at the state veterinary head quarters at the end of each month and them resubmitted to the FLD zonal office as monthly clinical report. Available data contained yearly and monthly treatment figures of the different diseases encountered at the clinics.

Data analysis

A part of the above data dealing specifically with trypanosomosis, PPR and bronchopneumonia were analyzed. All the data were entered into the computer and subsequently analyzed using the StatView (1996) and MS Excel 2000 package for windows. Overall, yearly, monthly and seasonal trends were computed using descriptive and quantitative analyses. The former involved the use of simple averages to determine trends across years, months and four seasons namely, Early dry (ED, October to December), Late dry (LD, January to March), Early wet (EW, April to June) and (LW, July to September). These were further subjected to analysis of variance (ANOVA) and where significant differences were observed, means were separated using the Least Significant Difference (LSD). The monthly means were also subjected to simple correlation statistics to determine possible relationships between data for the different diseases.

Climatic data for the state such as monthly means of daily air temperature, rainfall and relative humidity for the period under study were obtained from the weather station at Alvan Ikoku College of Education Owerri. The modulating effects of these climatic factors on monthly disease trends were graphically determined.


Results

Monthly means of rainfall, relative humidity and air temperature for the period under study are shown in Figures 1, 2 and 3.

Figure 1: Monthly variation in rainfall at Alvan Ikoku College of Education Owerri, Imo State Figure 2: Monthly variation in relative humidity at Alvan Ikoku College of Education Owerri, Imo State
Figure 3: Monthly variation in mean temperature at Alvan Ikoku College of Education Owerri, Imo State Figure 4. Monthly occurrence of trypanosomosis, bronchopneumonia and PPR among WAD goats
brought for treatment at government veterinary clinic in Imo State from 1999-2001

Overall yearly incidence of trypanosomosis, PPR and bronchopneumonia in WAD goats brought to government veterinary clinics in Imo state from 1999 to 2001 is shown in Table 1.

Table 1:  Overall yearly incidence of trypanosomosis, PPR and bronchopneumonia in WAD goats brought to Imo state government veterinary clinics from 1999 to 2001

Years

No (%) Tryps.

No (%) PPR

No (%) Bronch.

Total

SEM

1999

5475a(54.3)

1762b(17.5)

2853ab(28.3)

10090

1101.8

2000

5905a(58.9)

1784b(17.8)

2327ab(23.2)

10018

1234.7

2001

3444a(51.7)

  1679ab(25.2)

1534b (23.0)

  6657

  613.9

Total

14824a(55.4)

5225b(19.5)

6714ab(25.1)

26763

2982.6

Means

4941

1741

2238

8921

 

ab means on the same row without superscripts in common are different (p<0.05)

The overall seasonal influence on the occurrence of clinical cases of these diseases is presented in Table 2.

Table 2: Overall seasonal influence on the occurrence of clinical cases of trypanosomosis, PPR and bronchopneumonia among WAD goats brought for treatment at government veterinary clinics in Imo state, Nigeria from 1999 to 2001

Seasons

No (%) Tryps.

No (%) PPR

No (%) Broncho.

Total

LDS

3500b(23.6)

1313a(25.1)

2252a(33.5)

7065

EWS

3349b(22.6)

1353a(25.9)

1443b(21.5)

6145

LWS

3600b(24.3)

1191b(22.8)

1347b(20.1)

6138

EDS

4375a(29.5)

1368a(26.2)

1672ab(24.9)

7415

Total

14824(55.4)

5225(19.5)

6714(25.1)

26763

SEM

228

40.1

203

 

ab means on the same column without superscripts in common are different (p<0.05)

Simple correlation matrix of monthly means of disease occurrence is further presented in Table 3.

Table 3: Simple correlation matrix of mean monthly occurrence of clinical cases of trypanosomosis, bronchopneumonia and PPR among WAD goats at government veterinary clinics in Imo state, Nigeria from 1999-2001

 

Diseases

Trypanosomosis

Bronchopneumonia

PPR

 

Trypanosomosis

1.000

0.410

0.235

Bronchopneumonia

0.410

1.000

  0.440

 

PPR

0.235

0.440

  1.000

 

P<0.001   

 

These trends are further highlighted in Figure 4, which depicts the graphs of monthly mean occurrences of the diseases.


Discussion

The present results have shown that trypanosomosis, PPR and bronchopneumonia are important disease problems of WAD goats in Imo state, Nigeria. Clinical cases of these conditions occurred monthly with cases of trypanosomosis being higher at any time. Several published abattoir, clinical and field reports have highlighted the importance of these diseases among ruminants grazing the humid tropical zones of Nigeria (Akerejola et al 1979; Okolo 1985; Opasina 1985; Kalu et al 1991; Onyekweodiri and Uzoukwu 1992; Agu and Amadi 2001; Okoli 2001).

The present clinical record analysis for Imo state however, highlights the importance of trypanosomosis as a major natural infection of WAD goats in the state. This is interesting since published reports based on field blood sampling tend to restrict the incidence rate of the disease to between 2 and 10% (Fakae and Chiejina 1993; Onyia 1997; Agu and Amadi 2001). Before the experimental and epidemiological reports of Leeflang (1975), Ikede and Losos (1972) and Anosa and Isoun (1974), the disease was actually regarded as unimportant in small ruminants (Spephen 1970). The present result tends to agree more with the 51.6% and 33.3% prevalence rates reported in sheep and goats respectively at Gboko area of Benue state, Nigeria (Kalu et al 1991). A recent sero-prevalence study employing the standard direct sandwich technique of ELISA showed that of 320 sheep and goats blood samples assayed in Ondo and Ekiti states, Nigeria, 47.8%, 46.6% and 47.18% have had previous contact with either Trypanosoma brucei, Trypanosoma congolense orTrypanosoma vivax respectively (Osho et al 2002). Trypanosomosis seems to be remerging as a very important livestock disease in Nigeria, assuming major clinical importance in small ruminants and extending to previously designated tsetse free zones (Agu et al 1989; Kalu et al 1991; Kalejaiye and Omotosho 2000; Anosike et al 2002). The reasons for this need to be investigated.

Simple correlation matrix of the monthly occurrence of the three disease conditions showed that trypanosomosis and bronchopneumonia occurred together about 41% of the times; while for PPR and bronchopneumonia it was 44%. Bronchopneumonia of small ruminants is a bacterial infection caused mostly by Pasteurella organisms, especially Pasteurella histolytica, which exits saprophytically on the mucosa of upper air passages of the respiratory tracts. They become pathogenic under environmental and other stress-causing influences such as viral and parasitic infections (Jensen 1974; Seifert 1996). Other aerobic bacterial agents such as Pasteurellamultocida, Staphylococcus aureus, Streptococcus pyogenes, Corynebacterium pyogenes andBacillus sp. among others have been shown to play important roles in small ruminant pneumonia in Nigeria (Adekeye 1984; Obi 1997; Raji et al 1999). These bacteria usually find their way into underlying epithelial surfaces of pneumonic lungs damaged by viral or parasitic agents and hence complicate the infection (Adekeye 1984; Al-Tarazi and Daghall 1997). This probably explains the moderate association observed in the present study between clinical cases of PPR and bronchopneumonia.

Furthermore, secondary bacterial infections are associated with the chronic debilitating course and immunosuppressive nature of trypanosomosis (Jayawardena and Waksman.1984, Brown and Losos 1977). In a recent study by Okoli et al (2000), bronchopneumonia was reported as the sole complicating condition during pre and post treatment periods of experimental ovine trypanosomosis. The moderate association between trypanosomosis and bronchopneumonia in naturally infected WAD goats reported here is therefore expected and agrees with previous reports (Seifert 1996).

The present study shows that rainfall, relative humidity and mean daily air temperature have modulating effects on the occurrence of the three disease conditions in Imo state Nigeria. The relatively lower incidence of trypanosomosis observed during the heavy rainfall, high relative humidity and lower daily air temperature months of June to September are probably reflecting the bionomics of the glossina vectors of the disease. Ambient temperature and relative humidity among others are important limiting factors on the feeding intervals and pupall periods of the glossina (Seifert 1996). Furthermore, the sharp drop in disease occurrence from May to June may be due to the intense bush clearing and burning activities in the study area during this period. Bush burning for agricultural purposes opens up woodlands and forests thus destroying the habitat of the tsetse flies thereby limiting their ability to survive and transmit disease (Agu and Amadi 2001).

Higher incidence of PPR observed here during the dry months of December and January agrees with earlier reports by Obi (1983) and Onyekweodiri and Uzoukwu, (1992). The dusty and dry Hamattan wind that characterizes this period of the year has been shown to enhance the spread of PPR (Obi 1983). Bronchopneumonia was also significantly higher during the dry months. The moderate association observed between it and PPR may have driven this. Since the animals also showed relatively higher incidence of PPR during the same dry months, it is probable that the saprophytic organisms in the air passages responsible for the initiation of pneumonia became pathogenic because of the stress of PPR (Seifert 1996; Al- Tarazi and Daghall 1997).


Conclusion

Trypanosomosis, PPR and bronchopneumonia are important naturally occurring infections of WAD goats in Imo state. The present study reports moderate association between natural occurrences of the diseases in the study area. Contrary to published reports, trypanosomosis remained the most commonly encountered infection throughout the years, seasons and months studied. In-depth studies are needed to further elucidate the status of trypanosomosis of small ruminants in the humid tropics. Concurrent treatment against trypanosomosis and bronchopneumonia or PPR and bronchopneumonia is recommended since the present study has shown some reasonable association between their occurrences.


Acknowledgement

The author wishes to express his appreciation to Mr. Ifeanyi Nwogwugwu of the public health unit of the FLD, Imo state zonal office and Mr. Chukwuma of Alvan Ikoku College Of Education Owerri weather station for assistance in identifying the various clinical and weather records for this study.


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Received 9 April 2003; Accepted 11 August 2003

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